1. Field of the Invention
Exemplary embodiments of the present invention relate to a method and apparatus for transmitting/receiving packet in a wireless communication system.
2. Description of Related Art
While a variety of high-capacity multimedia services have been activated, the performance of a wireless communication system is not so high. Since multiple users share a wireless resource, the transmission rate of a wireless service, which is felt by the users, significantly decreases. Accordingly, research has been conducted on a variety of technologies which are to increase the performance of a wireless communication system for multiple users by increasing a bandwidth to expand the wireless resource shared by the multiple users or implementing a specific beam in communication with each of the users while using a wireless resource at the same bandwidth.
Since the medium access control (MAC) protocol of the wireless communication system operates based on carrier sense multiple access/collision avoidance (CSMA/CA), the MAC protocol contains a problem of resource waste which occurs during a channel contention process. In order to solve such a problem, burst transmission has been proposed. In the burst transmission, the enhanced MAC protocol defined in the IEEE 802.11e transmits multiple MAC protocol data units (MPDUs) at a short inter-frame space (SIFS) during a transmission opportunity (TXOP), when acquiring a transmission opportunity for a wireless resource, and receives a block ACK for the transmitted MPDUs. Furthermore, the IEEE 802.11n defines an aggregated MAC service data unit (A-MSDU) and an aggregated MPDU (A-MPDU), in order to aggregate MPDUs and MPDUs to transmit through one contention process for a wireless resource without an IFS.
According to the development trend of the above-described wireless communication system, the IEEE 802.11ac defines that a MAC service access point (MAC SAP) of an AP in a wireless communication system including one AP and two stations (STAs) should support the maximum performance of 1 Gbps and a MAC SAP of an STA for a point-to-point environment requires the maximum performance of 500 Mbps, in order to construct a high-speed wireless communication system. Furthermore, a characteristic in which the AP and the STA may simultaneously support the compatibility with the existing wireless communication system (IEEE 802.11a/n system) is defined as a requirement of the high-performance wireless communication system.
In a wireless communication system, an apparatus (AP or STA) which is to transmit data acquires a wireless channel, and then transmits data with information required for data transmission. A structure including data and information required for data transmission is referred to as a packet. At this time, the information required for data transmission is defined as an appointed value in a header.
FIG. 1 shows the format of a packet defined in the IEEE 802.11a. Data having a unit length of predetermined bytes are constructed with short/long training fields 110 and 120, a signal field 130, a service field 142, and tail/padding 144, which contain information required by a physical layer (PHY), and then transmitted to a receiver. The receiver receives data by using information acquired from the received fields. At this time, the data which are contained in a data field 140 with the service field 142 and the tail/padding 144 have a variable length within the maximum range.
FIG. 2 shows a packet having a mixed format which may be received by both of the IEEE 802.11a system and 802.11n system. Referring to FIG. 2, the packet having a mixed format includes a legacy field 210 consisting of a legacy-short training field (L-STF), a legacy-long training field (L-LTF), and a legacy-signal field (L-SIG) such that the 802.11a system may acquire information for receiving data. Furthermore, the packet includes a field 220 for the 802.11n system from a HT-SIG field such that the 802.11n system may acquire information required for receiving data.
As the wireless communication systems such as the 802.11a system and the 802.11n system define the packet formats as shown in FIGS. 1 and 2, there is demand for a packet format coinciding with a high-performance wireless communication system capable of simultaneously transmitting different packets to multiple users, for example, a wireless communication system based on multi-user multi-input multi-output (MU-MIMO).